Outline

Purpose: To evaluate the influence of bone cement in the path of proton beam on its range and on dose distribution.

Methods and materials: Two computed tomography (CT) data sets were obtained with and without a bone cement disk placed in a water phantom. Treatment planning was performed on a set of pristine CT images with 1.14-cm-thick bone cement disk, and the verification plan was applied to the same set of CT images with a corrected CT number for the bone cement disk. The corrected CT number was determined by the measurement of an actual proton range with the bone cement disk.

Results: The corrected CT number was given by 260 Hounsfield units (HU). The proton range calculated for pristine CT data of bone cement without any correction was 8.9 mm shorter than that calculated for corrected CT data with the CT number corresponding to the real stopping power of the bone cement disk. The measured proton range was also 8.9 mm longer than the calculated range for pristine CT data when the measured proton range in water was matched to the calculated one. On the contrary, the measured proton range coincided with the calculated range for corrected CT data in water.

Conclusion: We found that the heterogeneity of bone cement could cause an incorrect proton range in a treatment plan based on CT images. An effective CT number of bone cement was determined for more actual proton range calculation.